I'm working on a 86 740 4 cyl, no turbo. Cranks, but won't start. Would occationally, apparently randomly, work fine for 10 minutes then fail. Hasn't even done that for a while.

The fuel pump doesn't go on, but will if you manually push the relay. (I took the cover off the relay). The lamda sond (or whatever it's called) relay right next to the fuel pump relay does engage on its own.

There's no spark. I removed the distributor and the HAL sensor was very dirty and oily. I cleaned it well, but that didn't solve the problem. The distributor does spin.

I assume it's the coil or the HAL thing in the distributor. I couldn't figure out anything else. We're on a very tight budget at it would be nice to close in on the problem before buying parts.

Can I test the coil by putting voltage across it to manually generate a spark? Can I test the HAL thing some way?

I can get a coil for $5 or so at a junk yard and a whole distributor for $25. Sounds cheap, but if I could know the problem first, then it would be worth it. $25 on a guess will hurt.

Anyway to test those items, or maybe something I didn't think of?

Thanks,

John

 

My guess would be either the Dist. or the Power stage.

 

You can check the three wires on the hall pickup. With the key in the on position you should have 12v on one terminal one terminal is ground and one terminal will be 0v or 5v depending where the disk is. This signal wire can be checked for pulse while cranking with a logic probe. I second the tech. Working sometimes and not working again when warm seem to be hall pickup. They are expensive $90 ! for the hall pickup. Tap the fuel pump relay a few times and see if it starts, if it does replace the relay. Let us know what you find.

 

My 86' 740 gle had same issues, I eventually after doing some tests it led back to a bad ICU unit under driver side dash. Black box. I purchased used one from eBay for 30.00 and started right up. Bad hall sensor in distributor will not only cause no spark but also if there is no spark signal to ICU it will also not turn on your fuel pump relay.